1. Field of the Invention
This invention relates generally to implanted spinal fixation devices, and more particularly to a split eyebolt used on a spinal rod to secure a hook or other attachment device at any of various desired possible locations on the spinal rod.
2. Description of the Prior Art
In connection with certain corrective work for human spinal columns, spinal rods are disposed on both sides of the spinal column. Various types of attaching devices are placed along the length of the spinal rods and connected to the vertebrae in various ways. An example of such a device is shown in U.S. Pat. No. 4,648,388, issued on Mar. 10, 1987 to Steffee. This patent discloses "force transmitting members" 52 which are screwed into vertebrae and to which clamps are mounted. A spinal rod is placed in and secured to the clamps by tightening a nut on the end of the member 52 opposite that which is screwed into the vertebrae, thereby clamping the vertebrae to the spinal rod. Another arrangement, and which uses several types of hooks, rather than screws, for attachment to vertebrae, is shown in U.S. Pat. No. 4,641,636 issued on Feb. 10, 1987 to Cotrel. Another arrangement also using various types of hooks, but with an eyebolt on the rod to secure the hooks, is the "three-point shear" system of Danek Medical, Inc. Sometimes, during the course of the spinal implant operation, it can become evident that it is necessary or, at least, desirable to locate a fixation device someplace other than where previously thought necessary. In some instances it may be desirable to add a device or delete a device. With the type of arrangements shown in the aforementioned patents, that can be very inconvenient. With the Danek three-point shear system, although hooks can be readily added, prior to the present invention it was not so convenient to add eyebolts, because it was necessary to install them from one or the other end of the rod. The present invention was made in recognition of a need to provide some means to attach hooks or other anchoring devices to spinal rods and which can be installed between existing devices already attached to the spinal rods, and which also can be moved readily along the spinal rod during an implant procedure to place it in precisely the location desired without detaching the other devices.